Available online at ScienceDirect. Procedia Engineering 162 (2016 )

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1 Available online at ScienceDirect Procedia Engineering 162 (2016 ) International Conference on Efficient & Sustainable Water Systems Management toward Worth Living Development, 2nd EWaS 2016 Seasonal variation of soil moisture in irrigated olive trees Nektarios Kourgialas a, Georgios Doupis a, Androniki Papafilippaki a, Georgios Psarras a, Georgios Koubouris a, * a ELGO DEMETER, NAGREF, Institute for Olive Tree, Subtropical Crops and Viticulture, Agrokipio, Chania, Greece. Abstract Olive growing counts as one of the most significant agricultural activities in Greece, from a financial, social and ecological point of view. Modern olive culture often includes exhaustive use of the available water resources having as a result adverse effects for production cost and the environment. This paper evaluates seasonal soil moisture content at three different soil depths (10, 30, 40 cm), in relation with rainfall and irrigation in an olive cultivar Kalamon orchard. Our results indicate strong variation of soil moisture as affected by season and irrigation. In addition, the role of drip-irrigation on soil moisture content appears to be more significant at soil depths up to 30 cm compared to lower soil zones. Specifically, at soil depth of 40 cm the soil moisture curves close to irrigation lines seems to coincide compared to these far away from the irrigation line The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 2016 The Authors. Published by Elsevier Ltd. ( Peer-review under responsibility ofthe organizing committee of the EWaS2 International Conference on Efficient & Sustainable Peer-review under responsibility of the organizing committee of the EWaS2 International Conference on Efficient & Sustainable Water Systems Management toward Worth Living Development. Water Systems Management toward Worth Living Development Keywords:irrigation line; monitoring soil moisture; soil moisture with depth 1. Introduction One of the most important factors that can limit crop production is the limitation of water. [1,2] [3-6] Consequently, soil water status * Corresponding author: Dr G. Koubouris; Tel: ; Fax: address: Koubouris@nagref-cha.gr The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the organizing committee of the EWaS2 International Conference on Efficient & Sustainable Water Systems Management toward Worth Living Development doi: /j.proeng

2 472 Nektarios Kourgialas et al. / Procedia Engineering 162 ( 2016 ) monitoring is essential for evaluating soil water dynamics, for scheduling irrigation events and for supporting optimum plant growth and yields. According to [7] the application of the various soil water sensing and measurement systems (gravimetric analysis of soil samples, weighing lysimeters, capacitance probes, time domain reflectometry tensiometers) in commercial farms (although costly, time and labor consuming and not entirely precise due to technological or spatial constraints) is essential in order to have a real-time diagnostic tool for assessing the irrigation needs and for minimizing water drainage, nutrient leaching, and groundwater contamination. The capacitor usually takes the form of a polycarbonate cylinder with electronic sensors arranged at fixed intervals along its length. The probe uses electromagnetic signals to measure the permitivity of the soil, which is dominated by water, and implements a calibration curve of the measured electrical value against volumetric soil water content. Although, there is a considerable disagreement amongst authors as to the accuracy of the method, [8] and [9] reported that the capacitance probe method (CPM) is independent of soil type within a wide range of soil moisture levels. On the other hand, according to [10] and [11] the capacitance probe results are influenced by soil type, and in addition [12], [13] reported that capacitance probes are sensitive to soil salinity. The CPM method has been developed and used increasingly the last years, since it provides automatic acquisition of data at short time interval, minimal soil disturbance and enhancement of depth resolution. The aim of the present study was to investigate the spatial and temporal variation of soil moisture in a Mediterranean olive grove. Irrigation frequency and load could be optimized based on monitoring seasonal precipitation and water storage in the tree root zone in the soil. Consequently, water used for irrigation will be distributed more efficiently during the dry season and losses through evaporation or drainage will be reduced. 2. Methodology In this study 3 plots with 4 olive trees cv Kalamon each were selected in order to measure soil moisture at three different soil depths (10, 30, 40 cm). In each plot traditional agricultural practice of soil tillage was applied. Each plot has an area of 200 m 2. A typical plot scheme indicates the positions of soil measurements one close to irrigation-line (approximately 30 cm) and one far away from drip irrigation-line (in the centre of the plot), (Fig. 1). This experiment was designed in order to investigate the influence of irrigation on soil moisture content based on time and different soil depths. Apart from soil moisture rainfall was measured. The rainfall data that were used came from a surrounding meteorological station. Volumetric soil moisture content was assessed using a commercial PR2 profile probe system (Delta-T 2005). The PR2 was combined with an HH2 readout unit which enables a single probe to be used at different locations of the study area. Soil moisture measurements took place from May 2013 up to August 2014 at 20 days intervals, in order to capture the variability of soil moisture content based on different meteorological conditions. Regarding the irrigation season (May to September) drip irrigation was applied for one day every week, while moisture measurements took place after the applied irrigation. All plots have the geomorphological characteristics with same soil type which is characterized as sandy clay loam. In this study the seasonal soil moisture content with soil depth close to and far away (centre of the plot) from drip irrigation-lines was investigated and analyzed based on rainfall data. 3. Results and Discussion Figure 2 shows the seasonal rainfall during the experimental period while analysis of seasonal soil moisture content profile for 3 soil depths (10, 30 and 40 cm) is presented in Figure 3. Our data revealed a systematic variation of seasonal rainfall in the area under study characterized by a marked excess of precipitation during winter and spring and a significant deficit during summer, whereas autumn rainfall shows a great variability in trends. Differences in soil wetness in the first soil depth (10 cm) between Summer 2013 and Summer 2014 could be related to the higher precipitation values observed during the Spring of During periods of high rainfall, higher moisture values in the soil profile were recorded in the deeper layers (30 cm and 40 cm) away from drip irrigationline, while during the low rainfall period (irrigation period), a clearly increased response of volumetric soil water content to the position of soil moisture measurement was observed, since capacitance probes reported higher values close to the irrigation-line. When comparing soil moisture at the different depths, the deepest layer (40 cm) showed

3 Nektarios Kourgialas et al. / Procedia Engineering 162 ( 2016 ) the greatest soil moisture content, followed by the intermediate layer (30 cm) and the surface layer (10 cm), irrespective of the season of the measurement. Fig. 1. A typical plot scheme with irrigation-lines and soil moisture measurement positions. From our data, we also observed that there exists a significant influence of rainfall in soil moisture content with seasonally changing characteristics, since in addition to the rainfall-soil moisture connection during the wet season (winter-autumn), as expected, we also found significant correlation in summer when the precedent spring was characterized by high rainfall. Fig. 2. Seasonal rainfall data for the studied olive grove. We also would like to highlight that during the dry season, in addition to the depletion of soil water of the surface layer (10 cm), a deep soil water uptake (30 cm and 40 cm) was also observed. The higher soil moisture content

4 474 Nektarios Kourgialas et al. / Procedia Engineering 162 ( 2016 ) recorded at the center of the plot as compared to the value near the irrigation-line during the wet seasons could be ascribed to the rainfall interception at the tree canopy level. Research is ongoing to comprehend the effects of rainfall and irrigation in the soil moisture profile in years of different climatic characteristics. Irrigation frequency and load could be optimized based on monitoring seasonal precipitation and water storage in the tree root zone in the soil. Consequently, water used for irrigation will be distributed more efficiently during the dry season and losses through evaporation or drainage will be reduced. Especially in years such as with historically high temperature levels and low precipitation levels it is of great importance to optimize water use efficiency in agriculture. Fig. 3. Soil moisture content at (a) 10 cm; (b) 30 cm; (c) 40 cm soil depth under irrigated or rainfed conditions. Each bar is mean ± standard error for each treatment. Bars with the (*) were significantly different at p<0.05. Acknowledgements With the contribution of the LIFE + financial instrument of the European Union in the project OLIVECLIMA. References [1] J.A. Gómez, M. Amato, G. Celano, G. Koubouris, Organic olive orchards on sloping land: more than a specialty niche production system?, J. Environ. Manage. 89 (2008) [2] N.N. Kourgialas, G.C. Koubouris, G.P. Karatzas, I. Metzidakis, Assessing water erosion in Mediterranean tree crops using GIS techniques and field measurements: the effect of climate change, Nat. Hazards (2016) DOI /s

5 Nektarios Kourgialas et al. / Procedia Engineering 162 ( 2016 ) [3] G.C. Koubouris, N. Tzortzakis, N. Kourgialas, M. Darioti, I.T. Metzidakis, Growth, photosynthesis and pollen performance in saline water treated olive (Olea europaea L.) plants under high temperature, Int. J. Plant Biol. 6:6038 (2015) [4] G.C. Koubouris, N. Kavroulakis, I.T. Metzidakis, M.D. Vasilakakis, A. Sofo, Ultraviolet-B radiation or heat cause changes in photosynthesis, antioxidant enzyme activities and pollen performance in olive tree, Photosynthetica 53 (2015) [5] G.C. Koubouris, I.T. Metzidakis, M.D. Vasilakakis, Influence of cross pollination on the development of parthenocarpic -shotberries- olive (Olea europaea L.) fruits, Exp. Agric. 46 (2010) [6] G.C. Koubouris, I.T. Metzidakis, M.D. Vasilakakis, Impact of temperature on olive (Olea europaea L.) pollen performance in relation to relative humidity and genotype, Environ. Exp. Bot. 67 (2009) [7] S.R. Evett, R.C. Schwartz, J.J. Casanova, L.K. Heng, Review: Soil water sensing for water balance ET and WUE, Agric. Water Manag. 104 (2012) 1 9. [8] A.M. Thomas, In situ measurement of moisture in soil and similar substances by `fringe' capacitance, J. Sci. Instr. 43 (1966) [9] T.J. Hoekstra, A. Delaney, Dielectric properties of soils at UHF and microwave frequencies, J. Geophys. Res. 79 (1974) [10] V. Kuraz, J. Matousek, A new dielectric soil moisture meter for field measurement of soil moisture, Int. Comm. Irrig. Drain. (ICID) Bulletin 26 (1977) [11] J.P. Bell, T.J. Dean, M.G. Hodnett, Soil moisture measurement by an improved capacitance technique, part 2. Field techniques, evaluation and calibration, J. Hydrol. 93 (1987) [12] R.M. Mead, J.E. Ayars, J. Liu, Evaluation of the Sentek EnviroSCAN RT5 capacitance probe: laboratory calibration and field analysis, Water Manag. Res. Lab. ARS-USDA, Fresno, California, USA, [13] S.R. Evett, J.L. Steiner, Precision of neutron probe scattering and capacitance type soil water content gauges from field calibration, Soil Sci. Soc. Amer. J. 59 (1995)